UNITED NATIONS (Reuters) – United Nations Secretary-General Ban Ki-moon said on Saturday he was "deeply dismayed" by the execution of a prominent Shi'ite Muslim cleric and 46 other people in Saudi Arabia and called for calm and restraint.

Saudi Arabia executed cleric Nimr al-Nimr and dozens of al Qaeda members on Saturday, signaling it would not tolerate attacks, whether by Sunni jihadists or minority Shi'ites. The executions stirred sectarian anger across the Middle East.

"Sheik al-Nimr and a number of the other prisoners executed had been convicted following trials that raised serious concerns over the nature of the charges and the fairness of the process," Ban's spokesman said in a statement.

Ban had raised Nimr's case with Saudi leaders on a number of occasions and urged Saudi Arabia to commute all death sentences that had been imposed, the spokesman said.

"The Secretary-General also calls for calm and restraint in reaction to the execution of Sheikh Nimr and urges all regional leaders to work to avoid the exacerbation of sectarian tensions," the spokesman said.

Iranian protesters stormed the Saudi Embassy in Tehran early on Sunday as Shi'ite Muslim Iran reacted with fury to Sunni Saudi Arabia's execution of Nimr.

Ban "deplores the violence by demonstrators against the Saudi Embassy in Tehran," his spokesman said.